/*
ID: pallab81
PROG:
LANG: C++
*/

//"I have not failed, I have just found 10000 ways that won't work.

#include <iostream>
#include <algorithm>
#include <vector>
#include <sstream>
#include <fstream>
#include <string>
#include <list>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <functional>
#include <bitset>
#include <iomanip>

#include <ctime>
#include <cassert>
#include <cstdio>
#include <cmath>
#include <cstring>
#include <climits>
#include <cstdlib>

using namespace std;

#define VI vector< int >
#define CI( x ) scanf("%d",&x)
#define CL( x ) scanf("%lld",&x)
#define CD( x ) scanf("%lf",&x )
#define foR(i1,st,ed) for(int i1 = st,j1 = ed ; i1 < j1 ; ++i1 )
#define fo(i,ed) foR( i , 0 , ed )
#define foE(i,st,ed) foR( i , st , ed+1 )
#define foit(i, x) for (typeof((x).begin()) i = (x).begin(); i != (x).end(); i++)
#define bip( X ) sleep( X )
#define Int long long
#define pb push_back
#define SZ(X) (int)(X).size()
#define LN(X) (int)(X).length()
#define mk make_pair
#define f first
#define s second
#define SET( ARRAY , VALUE ) memset( ARRAY , VALUE , sizeof(ARRAY) )
#define line puts("")

template<class T1>
inline void debug(T1 _x) {
    cout<<_x<<'\n';
}
template<class T1, class T2>
inline void debug(T1 _x,T2 _y) {
    cout<<_x<<' '<<_y<<'\n';
}
template<class T1, class T2, class T3>
inline void debug(T1 _x,T2 _y,T3 _z) {
    cout<<_x<<' '<<_y<<' '<<_z<<'\n';
}
template<class T1, class T2, class T3, class T4>
inline void debug(T1 _x,T2 _y,T3 _z,T4 _zz) {
    cout<<_x<<' '<<_y<<' '<<_z<<' '<<_zz<<'\n';
}
template< class T1>
inline void debug(T1 _array,int _size) {
    cout<<"[";
    for (int i=0;i<_size;++i) {
        cout<<' '<<_array[i];
    }
    puts(" ]");
}

class NetworkXMessageRecovery {
public:
	string recover(vector <string> messages);
};

inline string toposort(set<char> all, vector< set<char> >req ){
    string ret="";
    set<char>::iterator pos;
    while( SZ(all)>0 ){
        foit(it, all){
            char cur=(*it);
            //if no requirments for this charecter
            if( !(SZ(req[cur])>0) ){
                ret+=cur;
                all.erase(cur);
                    //clear this letter from all nodes char required it
                    foit(itt,all){
                        char tmp=(*itt);
                        if( ( pos=req[tmp].find(cur) ) !=req[tmp].end() ){
                            req[tmp].erase(pos);
                        }
                    }
                break;
            }
        }
    }
    return ret;
}
string NetworkXMessageRecovery :: recover(vector <string> messages) {
    set<char> all;
    vector< set<char> > req(200,set<char>() );

    fo(i,SZ(messages)){
        fo(j,LN(messages[i]))
            all.insert(messages[i][j]);
    }
    fo(k,SZ(messages)){
        string str=messages[k];
        for(int i=0;i<LN(str);++i){
            for(int j=i+1;j<LN(str);++j){
                req[ str[j] ].insert(str[i]);
            }
        }
    }

return toposort(all,req);
}
// BEGIN KAWIGIEDIT TESTING
// Generated by KawigiEdit 2.1.8 (beta) modified by pivanof
#include <iostream>
#include <string>
#include <vector>
using namespace std;
bool KawigiEdit_RunTest(int testNum, vector <string> p0, bool hasAnswer, string p1) {
	cout << "Test " << testNum << ": [" << "{";
	for (int i = 0; int(p0.size()) > i; ++i) {
		if (i > 0) {
			cout << ",";
		}
		cout << "\"" << p0[i] << "\"";
	}
	cout << "}";
	cout << "]" << endl;
	NetworkXMessageRecovery *obj;
	string answer;
	obj = new NetworkXMessageRecovery();
	clock_t startTime = clock();
	answer = obj->recover(p0);
	clock_t endTime = clock();
	delete obj;
	bool res;
	res = true;
	cout << "Time: " << double(endTime - startTime) / CLOCKS_PER_SEC << " seconds" << endl;
	if (hasAnswer) {
		cout << "Desired answer:" << endl;
		cout << "\t" << "\"" << p1 << "\"" << endl;
	}
	cout << "Your answer:" << endl;
	cout << "\t" << "\"" << answer << "\"" << endl;
	if (hasAnswer) {
		res = answer == p1;
	}
	if (!res) {
		cout << "DOESN'T MATCH!!!!" << endl;
	} else if (double(endTime - startTime) / CLOCKS_PER_SEC >= 2) {
		cout << "FAIL the timeout" << endl;
		res = false;
	} else if (hasAnswer) {
		cout << "Match :-)" << endl;
	} else {
		cout << "OK, but is it right?" << endl;
	}
	cout << "" << endl;
	return res;
}
int main() {
	bool all_right;
	all_right = true;

	vector <string> p0;
	string p1;

	{
	// ----- test 0 -----
	string t0[] = {"acd","bce"};
			p0.assign(t0, t0 + sizeof(t0) / sizeof(t0[0]));
	p1 = "abcde";
	all_right = KawigiEdit_RunTest(0, p0, true, p1) && all_right;
	// ------------------
	}

	{
	// ----- test 1 -----
	string t0[] = {"ed","dc","cb","ba"};
			p0.assign(t0, t0 + sizeof(t0) / sizeof(t0[0]));
	p1 = "edcba";
	all_right = KawigiEdit_RunTest(1, p0, true, p1) && all_right;
	// ------------------
	}

	{
	// ----- test 2 -----
	string t0[] = {"Fox","Ciel","FoxCiel"};
			p0.assign(t0, t0 + sizeof(t0) / sizeof(t0[0]));
	p1 = "FoxCiel";
	all_right = KawigiEdit_RunTest(2, p0, true, p1) && all_right;
	// ------------------
	}

	{
	// ----- test 3 -----
	string t0[] = {"a","A"};
			p0.assign(t0, t0 + sizeof(t0) / sizeof(t0[0]));
	p1 = "Aa";
	all_right = KawigiEdit_RunTest(3, p0, true, p1) && all_right;
	// ------------------
	}

	if (all_right) {
		cout << "You're a stud (at least on the example cases)!" << endl;
	} else {
		cout << "Some of the test cases had errors." << endl;
	}
	return 0;
}
// END KAWIGIEDIT TESTING


//Powered by KawigiEdit 2.1.8 (beta) modified by pivanof!
